[release/7.0] Fix two auto-atomicity Regex bugs #74834
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We walk concatenations in order to combine adjacent loops, e.g. `a+a+a+` becomes `a{3,}`. We also combine loops with individual items that are compatible, e.g. `a+ab` becomes `a{2,}b`. However, we're doing these operations on atomic loops as well, which is sometimes wrong. Since an atomic loop consumes as much as possible and never gives anything back, combining it with a subsequent loop will end up essentially ignoring any minimum specified in the latter loop. We thus can't combine atomic loops if the second loop has a minimum; this includes the case where the second "loop" is just an individual item.
We currently consider \w and \b non-overlapping, which allows a \w loop followed by a \b to be made atomic. The problem with this is that \b is zero-width, and it could be followed by something that does overlap with the \w. When matching at a location that is a word boundary, it is possible the first loop could give up something that matches the subsequent construct, and thus it can't be made atomic. (We could probably restrict this further to still allow atomicity when the first loop has a non-0 lower bound, but it doesn't appear to be worth the complication.)
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Tagging subscribers to this area: @dotnet/area-system-text-regularexpressions Issue DetailsBackport of #74726 to release/7.0 /cc @stephentoub Customer ImpactTestingRiskIMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.
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Approved. Correctness of core functionality |
joperezr
approved these changes
Aug 30, 2022
carlossanlop
approved these changes
Aug 30, 2022
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The CI failure was a cancellation/timeout. |
ghost
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Backport of #74726 to release/7.0
/cc @stephentoub
Customer Impact
Testing
Risk
IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.